A relatively recent development in the field of coatings and adhesives has been the development of a class of materials which we shall refer to as polymeric organosilanes. These materials comprise organic polymer backbones having hydrolytically reactive silyl groups pendent therefrom. These types of compounds can be conveniently produced by copolymerizing ethylenically unsaturated organic monomers, e.g. ethyl acrylate, vinyl acetate, and the like, with ethylenically unsaturated organosilane monomers having hydrolytically reactive groups bonded to the silicon, e.g. vinyltrimethoxysilane, .gamma.-methacryloxypropyltrimethoxysilane and the like. Examples of such copolymerized organosilanes are found in U.S. Pat. Nos. 3,408,420; 3,306,800; 3,542,585; 3,962,471; 3,062,242; and 3,577,399.
The polymeric organosilanes described above have been used as coating materials which displayed improved adhesion to inorganic oxide substrates by comparison to similar organic polymers containing no silyl groups. It has also been suggested that polymeric organosilanes be employed as adhesion promoters (i.e. coupling agents) to improve the bonding between a resinous medium and an inorganic substrate or filler (see, e.g., U.S. Pat. No. 3,306,800 and Inoue et al., J. Applied Polymer Sci., Vol. 19, pp. 1939-1954(1)
It has been further suggested that such polymeric organosilanes might impart bonding strength which is superior to that imparted by conventional monomeric silane coupling agents when employed in conjunction with non-reactive thermoplastic resins. Conventional monomeric silane coupling agents generally consist of silanes containing at least one reactive organic group and at least one hydrolyzable group bonded to the silicon atom. The monomeric silane coupling agents rely largely on the reactivity of their organic groups with coreactive organic groups in the resin matrix to provide bonding, hence, they do not function well in conjunction with resins such as thermoplastics containing no reactive groups. Polymeric organosilanes would be expected to provide improved bonding with thermoplastic resins due to the compatibility of the organic polymer portion with the thermoplastic resin matrix.
While polymeric organosilanes indeed provide improved bonding between thermoplastic resins and inorganic oxide substrates, it is clear that relatively high levels of silane monomer, on the order of 20 to 25 mole %, must be copolymerized in the polymeric organosilane in order to achieve optimum bond strength. Employing these high levels of silane, however, can cause problems for a number of reasons. From an economic standpoint, the silane is a relatively costly material, thus, considerable economic benefit would be obtained if the silane content of the polymeric organosilane could be reduced without loss of adhesive strength. Moreover, high levels of silane in the polymeric organosilane tend to make it unstable and reduce its potlife. This latter phenomenon is due to hydrolytic crosslinking reactions which occur at the silyl groups of the polymeric organosilane and can cause unacceptable increases in viscosity and even gelation when the material is exposed to ambient moisture. The high levels of silane which have been required in the prior art to optimize bond strength when the polymeric organosilane is employed as an adhesion promoter unfortunately increase the likelihood of premature crosslinking of the polymeric organosilane.